Smallpox Vaccine

The smallpox vaccine is made from caccinia, a virus related to, but different from, smallpox. Reports vary concerning the number of existing smallpox vaccine doses in the U.S. and abroad. Studies are under way to determine how much a vaccine dose can be diluted without compromising its effectiveness. The Department of Health and Human Services' goal is to have one dose for every American in case of a bioterrorism attack. Until then, the executive branch of the federal government, via the CDC, decides who is vaccinated. The state health departments also have access to limited local stock. Reports also vary concerning the World Health Organization's current storage of smallpox vaccine.

The smallpox vaccine and vaccinia immune globulin (VIG) are available only through the CDC and state health agencies. The calf lymph vaccine is the only one still available although a replacement vaccinia vaccine produced from cell cultures is under development.

Currently, the only licensed smallpox vaccine is Dryvax. However, several other vaccines are being assessed in clinical trials. The National Institute of Allergy and Infectious Disease has awarded two contracts to Acambis, Inc., to develop, test, and supply the U.S. with enough doses of smallpox vaccine to manage a potential outbreak in case of smallpox bioterrorism. Some studies on the existing American vaccine stockpiles indicate that the vaccine would be effective in dilutions of 1:10. However, the occurrence of the "take," a small scab that forms when a vaccination is successful, would be insufficient at this dilution to ensure eradication among an infected population. Further studies at 1:5 dilution are in progress. The FDA approved the newer Acambis-Sandofi vaccine (ACAM 2000) in 2008 to replace Dryvax.

The U.S. government is unlikely to restart a smallpox vaccination program anytime soon, even after obtaining enough vaccine to immunize everyone in the country. This is because the vaccine itself is dangerous to people with immunological disorders, such as HIV, or other immunocompromising conditions, such as certain forms of cancer.

The smallpox vaccine actually contains live viral particles of vaccinia, a virus similar to smallpox. This virus usually does not cause disease in humans. However, vaccination with this vaccine could prove deadly in a person with an impaired immunity because the virus is allowed to spread uncontrolled throughout the body. No one with a weakened immune system should receive the vaccine. People with the skin conditions such as eczema or atopic dermatitis should not have the vaccination because of the risk of rare but life-threatening reactions.

Most vaccine experts would only recommend a large-scale vaccination program if smallpox were released into the general population as a biological weapon. Vaccination of first responders to a smallpox outbreak has begun. President Bush received the vaccinia protection against smallpox in support of the U.S. troops receiving theirs.

Researchers estimate that of the previously vaccinated population, many probably retain some varying degree of residual immunity. This means that if an outbreak were to occur, some people vaccinated years ago, if exposed to smallpox, may respond by developing full-blown disease, mild disease, or no disease. How many years it has been since a person's last vaccination and, possibly, the total number of vaccinations an individual has received may determine that person's reaction to exposure to smallpox. Smallpox researchers usually are revaccinated every three years.